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PubMed2006

A diffusion model analysis of adult age differences in episodic and semantic long-term memory retrieval.

Two experiments investigated adult age differences in episodic and semantic long-term memory tasks, as a test of the hypothesis of specific age-related decline in context memory. Older adults were slower and exhibited lower episodic accuracy than younger adults. Fits of the diffusion model (R. Ratcliff, 1978) revealed age-related increases in non-decisional reaction time for both episodic and semantic retrieval. In Experiment 2, an age difference in boundary separation also indicated an age-related increase in conservative criterion setting. For episodic old-new recognition (Experiment 1) and source memory (Experiment 2), there was an age-related decrease in the quality of decision-driving information (drift rate). As predicted by the context-memory deficit hypothesis, there was no corresponding age-related decline in semantic drift rate.

Adolescent↗

PubMed2000

Is heterosynaptic modulation essential for stabilizing Hebbian plasticity and memory?

In 1894, Ramón y Cajal first proposed that memory is stored as an anatomical change in the strength of neuronal connections. For the following 60 years, little evidence was recruited in support of this idea. This situation changed in the middle of the twentieth century with the development of cellular techniques for the study of synaptic connections and the emergence of new formulations of synaptic plasticity that redefined Ramón y Cajal's idea, making it more suitable for testing. These formulations defined two categories of plasticity, referred to as homosynaptic or Hebbian activity-dependent, and heterosynaptic or modulatory input-dependent. Here we suggest that Hebbian mechanisms are used primarily for learning and for short-term memory but often cannot, by themselves, recruit the events required to maintain a long-term memory. In contrast, heterosynaptic plasticity commonly recruits long-term memory mechanisms that lead to transcription and to synpatic growth. When jointly recruited, homosynaptic mechanisms assure that learning is effectively established and heterosynaptic mechanisms ensure that memory is maintained.

Animals↗

PubMed1990

Long-term potentiation of electrotonic coupling at mixed synapses.

Long-term potentiation of chemical synapses is closely related to memory and learning. Studies of this process have concentrated on chemically mediated excitatory synapses. By contrast, activity-dependent modification of gap junctions, which also widely exist in higher structures such as hippocampus and neocortex, has not been described. Here we report that at mixed synapses between sensory afferents and an identified reticulospinal neuron, the electrotonic coupling potential can be potentiated, as well as the chemically mediated excitatory postsynaptic potential, for a prolonged time period using a stimulation paradigm like that which produces long-term potentiation in hippocampus. The effect on coupling is due to an increase in gap-junctional conductance. Our data indicate that the potentiation of both synaptic components requires an increase in intracellular calcium, involves activation of NMDA (N-methyl-D-aspartate) receptors, and is specific to the tetanized pathway.

Afferent Pathways↗

PubMed1995

Hippocampectomy impairs the memory of recently, but not remotely, acquired trace eyeblink conditioned responses.

New Zealand male rabbits (Oryctolagus cuniculus) were trained on a trace eyeblink conditioning paradigm using a 250-ms tone conditioned stimulus, a 100-ms airpuff unconditioned stimulus, and a 500-ms trace interval. Rabbits received bilateral hippocampal aspirations either 1 day or 1 month after learning. Controls consisted of time-matched sham-operated and neocortical aspirated rabbits. When retested on the trace paradigm, rabbits with hippocampal aspirations 1 day after learning were significantly and substantially impaired in the retention of trace conditioned responses. In contrast, rabbits that received hippocampal aspirations 1 month after training retained trace conditioned responses at a level comparable to that of the controls. Moreover, hippocampectomy had no effect on the retention of delay eyeblink conditioning. Thus, the hippocampus appears to be necessary for the retention of recently acquired, but not remotely acquired, trace conditioned responses.

Animals↗

PubMedDate not supplied

Do children still pick and choose? The relationship between phonological knowledge and lexical acquisition beyond 50 words.

Previous studies document an influence of phonological knowledge on word learning that differs across development. Specifically, children with expressive lexicons of fewer than 50 words learn words composed of IN sounds more rapidly than those composed of OUT sounds. In contrast, preschool children with larger expressive lexicons show the reverse effect. The goal of the current study was to provide a re-analysis of existing data to determine if this discrepancy across studies may be related to how phonological knowledge has been defined. This study defines knowledge on a continuum from most to more to less. Results showed a continuous inverse relationship between phonological knowledge and word learning by preschool children. Specifically, most phonological knowledge was associated with poorest word learning, more knowledge with intermediate word learning, and less knowledge with best word learning. Theoretical implications are discussed.

Child, Preschool↗

PubMed1993

Perceptual and cognitive spatial learning.

Ss were taught novel mappings between visual space and motor space with either a variant on a prism adaptation paradigm (Experiments 1 and 2) or a nonperceptual cognitive task (Experiments 3 and 4). First, discrimination training specified that 1 visual location required a new pointing response but another location did not. This led to unusual generalization unlike typical generalization decrement. Second, training at 9 locations specified that 1 location required a new response but that the remaining 8 did not. This simple isolation mapping was unlearnable and instead a flat function fit through all of space. In contrast, for the cognitive paradigm, not only was isolation of one region of space easily learned, it was the preferred pattern of generalization. Implications for perceptual learning, as well as the qualitative distinctions between perceptual and cognitive learning, are discussed.

Adult↗

PubMed2006

Motor learning of a dynamic balancing task after stroke: implicit implications for stroke rehabilitation.

BACKGROUND AND PURPOSE: After a stroke, people often attempt to consciously control their motor actions, which, paradoxically, disrupts optimal performance. A learning strategy that minimizes the accrual of explicit knowledge may circumvent attempts to consciously control motor actions, thereby resulting in better performance. The purpose of this study was to examine the implicit learning of a dynamic balancing task after stroke by use of 1 of 2 motor learning strategies: learning without errors and discovery learning. PARTICIPANTS AND METHODS: Ten adults with stroke and 12 older adults practiced a dynamic balancing task on a stabilometer under single-task (balance only) and concurrent-task conditions. Root-mean-square error (in degrees) from horizontal was used to measure balance performance. RESULTS: The balance performance of the discovery (explicit) learners after stroke was impaired by the imposition of a concurrent cognitive task load. In contrast, the performance of the errorless (implicit) learners (stroke and control groups) and the discovery learning control group was not impaired. DISCUSSION AND CONCLUSION: The provision of explicit information during rehabilitation may be detrimental to the learning/relearning and execution of motor skills in some people with stroke. The application of implicit motor learning techniques in the rehabilitation setting may be beneficial.

Adult↗

PubMed2001

The role of the avian hippocampus in orientation in space and time.

We examined the effects of hippocampus (Hp) and area parahippocampalis (APH) lesions in pigeons on their ability to perform a battery of tasks including autoshaping, time discrimination, spatial memory, and pattern discrimination. Pigeons with Hp-APH lesions were impaired in the acquisition of an autoshaped response, emitting fewer pecks to the stimulus than control animals. Hp-APH pigeons were also impaired in the acquisition of a radial-arm maze analogue task, and those birds that did learn the task seemed to do so by adopting a stereotypic response strategy. In contrast, Hp-APH lesions had no effect on the ability of the birds to discriminate on the basis of either temporal or visual information. Overall, these studies complement our earlier studies and suggest that the avian hippocampus is important for the processing and retention of spatial rather than non-spatial information.

Animals↗

PubMedDate not supplied

Analysis of the role of behavioural factors in the development of tolerance to the benzodiazepine midazolam.

Two experiments were conducted on the acute and chronic effects of the short-acting benzodiazepine midazolam on fixed ratio schedule-maintained operant responding in rats. Acute administration of midazolam produced suppression of responding in large doses but elevation of responding in small doses. Following intermittent (every third day) chronic treatment tolerance developed rapidly to the rate-suppressant effects of large doses of midazolam but did not develop to the rate-elevating effects of small doses, even after chronic treatment with large doses of the drug. Thus, when tolerance was measured in terms of shifts in dose-effect curves, it was manifested as a non-parallel shift in the curve after chronic treatment. Since tolerance developed to the effects of large but not small doses, the observed tolerance could not be attributed to changes in disposition of the drug. The development of tolerance did not depend on whether the drug was given before or after behavioural testing. These findings contrast with data reported in behavioural studies with other sedative-hypnotics (ethanol, barbiturates). Animals tolerant to midazolam showed no cross-tolerance to ethanol, a drug for which there is reliable evidence indicating that behavioural factors play a role in acquisition of tolerance. Tolerance to midazolam cannot therefore be explained in terms of learned strategies acquired as a result of drug-induced loss of rewarding stimuli. This conclusion contrasts with recent suggestions (File, 1985; File and Pellow, 1985) that tolerance to benzodiazepines may be mediated by instrumental conditioning processes.

Animals↗

PubMed1993

AF64A (ethylcholine mustard aziridinium) impairs acquisition and performance of a spatial, but not a cued water maze task: relation to cholinergic hypofunction.

The cholinergic neurotoxin AF64A (ethylcholine mustard aziridinium) produced alterations in a spatial but not a nonspatial cognitive task following ICV injection. AF64A impaired acquisition and performance in the standard Morris water maze task, evidenced by significantly longer latencies to find the submerged platform. However, the AF64A group exhibited shorter latencies and more direct paths to the target at the end of training, which suggests acquisition of efficient search strategies and a sparing of procedural memory. However, the AF64A group spent significantly less time in the target quadrant during the probe trial than the CSF group. This suggests a failure to learn the specific location of the target and impaired declarative memory processes. In contrast, AF64A did not affect performance of a cued MWM task that did not involve spatial memory processing, demonstrating the absence of motoric, sensory, or motivational impairments. The AF64A-induced behavioral deficits were associated with a) a significant decrease in high affinity choline transport (HAChT), b) reduced concentrations of 5-HT and 5-HIAA, and c) an increased ratio of 5-HIAA/5HT, in the HPC. There were no changes in choline uptake in the gustatory cortex, the amygdala, or the striatum. Percent time in the target quadrant during the probe trial was significantly correlated with HAChT in the HPC. There were no correlations between any of the behavioral measures and HAChT in the striatum, gustatory cortex, or the amygdala, or between serotonergic or noradrenergic parameters in the HPC. These data suggest that AF64A produces cognitive deficits in spatial tasks that are correlated with the cholinergic hypofunction induced by the compound.

Acetylcholine↗

PubMed1984

Contrasting effects of d-amphetamine on affiliation and aggression in monkeys.

Amphetamine has been observed to alter conditioned or learned behavior in individually housed animals, as well as naturally-occurring behavior characteristic of animals living in groups. This study is concerned with the effects of d-amphetamine on affiliative and aggressive behavior in adult male stumptail macaques (Macaca arctoides) living in a large, heterogeneous social group. Using standardized observational techniques, the affiliative and aggressive behaviors initiated by five adult male monkeys were characterized and quantitated in the absence of and following drug administration. Acute administration of a range of doses of d-amphetamine (0.003-0.56 mg/kg) resulted in a monotonically depressive effect on the rate of affiliative behavior initiated by the experimental animals. In contrast, d-amphetamine increased the rate of aggressive behavior initiated by the highest- and lowest-ranking monkeys, and had little or no effect in the mid-ranking monkeys. These results show that d-amphetamine can have qualitatively different effects on affiliative and aggressive behavior in the same subjects. The results also provide evidence that the effects of d-amphetamine can be determined by the hierarchical or dominance position of the subject in the group.

Aggression↗

PubMed2000

Learning deficiency and alterations in acetylcholine receptors and protein kinase C in the brain of senescence-accelerated mouse (SAM)-P10.

The senescence-accelerated mouse (SAM) is known to be a murine model for accelerated aging. A novel inbred SAMP10 has shown age-related brain atrophy and learning deficiency. In the present study, we investigated the changes in learning ability and in ligand binding with muscarinic acetylcholine (mACh) receptors, alpha adrenoceptors and protein kinase C in SAMP10. In Morris's water maze task, in a control strain of SAMR1 at 9 months, the escape latency and path length decreased with increasing trial days, in contrast, escape latency and path length did not decrease in SAMP10. These results indicate that SAMP10 exhibits learning deficiency. The ligand binding activity of mACh receptors decreased in the hippocampus of SAMP10 and the protein kinase C level in the hippocampus of SAMP10 was lower than that of SAMR1. On the other hand, there was no significant difference between SAMR1 and SAMP10 regarding ligand binding activity of alpha(1) and alpha(2) adrenoceptors. Thus, a reduction of mACh receptors and protein kinase C in the brain seems to underlie dysfunction of learning and memory in SAMP10.

Aging, Premature↗

PubMed1986

Caloric regulation in the rat: control by two factors.

These experiments demonstrate that rats can immediately adjust their meal size in response to variations in the caloric density of a novel diet. However, this immediate caloric sensitivity only seems to appear when rats have been adapted to small, calorically insufficient meals. Rats in Experiment 1 were given timed access to unlimited quantities of an oil/water diet during baseline, and they showed no indication of compensating for changes in the caloric density of the oil/water diet during a test meal. Instead, they consumed about the same amount they had consumed during the preceding baseline meal, suggesting that a learned habit of consuming a certain volume of food controlled their meal size. In contrast, rats that were accustomed to receiving only a very small quantity of food for one of their daily meals during baseline immediately responded to the caloric density of an oil/water test diet by consuming a larger meal if the diet was dilute than if it was calorically more concentrated (Experiments 2 and 3). This immediate sensitivity to caloric density occurred whether or not the rats were exposed to the oil/water diet during baseline, suggesting that rats have some way of directly "metering" the caloric density of new foods. Thus, rats' caloric intake during a meal appears to be controlled by two factors: under certain conditions, control is by caloric learning, under other conditions control is by a caloric metering mechanism.

Adaptation, Psychological↗

PubMed1982

Hemispheric asymmetry for face recognition: some effects of visual masking, hemiretinal stimulation and learning task.

Five overlearned target faces were presented hemiretinally and identified by name on the recognition trials (Experiment 1). A post-exposure pattern mask was projected by the opposite eye to either the same (MASK) or the opposite (DISTRACTOR) hemisphere as the targets. Target exposure durations yielding 50% accuracy showed significant left-hemisphere and temporal hemiretinal superiorities in DISTRACTOR, but not in MASK. In Experiment 2, recognition accuracy for six faces at a constant exposure duration, under DISTRACTOR and no-mask control conditions, replicated the left-hemisphere advantage. Manipulation of the information accompanying targets during the initial learning task, to encourage either "social" or "physical" encoding of the faces, produced a "crossover" pattern of contrasting hemispheric asymmetries under the two encoding conditions. The overall results suggest that within this design, face recognition can be accomplished in three different ways, producing either no hemispheric asymmetry, undirectional asymmetry, or complex, contrasting asymmetries. These effects appear to have different functional loci. Hemiretinal differences and individual differences in encoding strategies also contributed to complex patterns of hemispheric asymmetry.

Adult↗

PubMed1998

Personal reflections on early learning in shared leadership.

Shared leadership involves a process as well as a structure. Two key principles apply to all forms of shared leadership: a commitment to true partnership and a decision-making structure that allows for balance of power. In this article, the author shares her personal experience of facilitating a shared leadership model for staff on a unit level and also an executive model of shared leadership. The executive model was implemented during a transition after a traditional nursing leadership position was vacated. Lessons learned in facilitating a staff shared leadership model and participating in an executive model are discussed and contrasted. Relationships, dialogue, partnership, and an understanding of boundaries are essential elements for successful implementation of shared leadership at any level.

Decision Making, Organizational↗

PubMed1995

The ascending neuromodulatory systems in learning by reinforcement: comparing computational conjectures with experimental findings.

A central problem in cognitive neuroscience is how animals can manage to rapidly master complex sensorimotor tasks when the only sensory feedback they use to improve their performance is a simple reinforcing stimulus. Neural network theorists have constructed algorithms for reinforcement learning that can be used to solve a variety of biological problems and do not violate basic neurophysiological principles, in contrast to the back-propagation algorithm. A key assumption in these models is the existence of a reinforcement signal, which would be diffusively broadcast throughout one or several brain areas engaged in learning. This signal is further assumed to mediate up- and downward changes in synaptic efficacy by acting as a multiplicative factor in learning rules. The biological plausibility of these algorithms has been defended by the conjecture that the neuromodulators noradrenaline, acetylcholine or dopamine may form the neurochemical substrate of reinforcement signals. In this commentary, the predictions raised by this hypothesis are compared to anatomical, electrophysiological and behavioural findings. The experimental evidence does not support, and often argues against, a general reinforcement-encoding function of these neuromodulatory systems. Nevertheless, the broader concept of evaluative signalling between brain structures implied in learning appears to be reasonable and the available algorithms may open new avenues for constructing more realistic network architectures.

Adaptation, Psychological↗

PubMed1998

Characterization of perforant path lesions in rodent models of memory and attention.

Early stage Alzheimer's disease (AD) pathology is associated with neurodegeneration of systems within the temporal cortex, e.g. the entorhinal cortex, perforant pathway and hippocampus. The perforant pathway provides the major neuronal input to the hippocampus from the entorhinal cortex and thus relays multimodal sensory information derived from cortical zones into the hippocampus. The earliest symptoms of AD include cognitive impairments, e.g. deficits in short-term memory and attention. Consequently, we have investigated the effect of bilateral knife cut lesions to the perforant path on cognition in rats using models measuring primarily short-term memory (operant delayed match to position task), attention (serial five-choice reaction time task) and spatial learning (Morris water maze). Rats receiving bilateral perforant path lesions showed normal neurological function and a mild hyperactivity. The lesion produced little effect on attention assessed using the five-choice task. In contrast, animals with equivalent lesions showed a robust delay-dependent deficit in the delayed match to position task. Spatial learning in the water maze task was also severely impaired. The delay-dependent deficit in the match to position task was not reversed by tacrine (3 mg/kg) pretreatment. The present data support a selective impairment of cognitive function following perforant path lesions that was confined to mnemonic rather than attentional processing. These findings complement primate and human studies identifying a critical role of the perforant pathway and associated temporal lobe structures in declarative memory. Degeneration of the perforant pathway is likely to contribute to the mnemonic deficits characteristic of early AD. The failure of tacrine to ameliorate these deficits may be relevant to an emerging clinical literature suggesting that cholinomimetic therapies improve attentional rather than mnemonic function in AD.

Animals↗

PubMed2001

Prenatal glucocorticoid programming of brain corticosteroid receptors and corticotrophin-releasing hormone: possible implications for behaviour.

Glucocorticoids may underlie the association between low birth weight and adult disorders such as hypertension, type 2 diabetes and affective dysfunction. We investigated the behavioural and molecular consequences of two paradigms of prenatal dexamethasone administration in rats. Rats received dexamethasone (100 microg/kg per day) throughout pregnancy (DEX1-3), in the last third of pregnancy only (DEX3) or vehicle. Both dexamethasone treatments reduced birth weight, only DEX1-3 offspring had reduced body weight in adulthood. In adult offspring, both prenatal dexamethasone paradigms reduced exploratory behaviour in an open field. In contrast, only DEX3 reduced exploration in an elevated plus-maze and impaired behavioural responses and learning in a forced-swim test. This behavioural inhibition may reflect increased baseline corticotrophin-releasing hormone mRNA levels (30% higher) in the central nucleus of the amygdala in both dexamethasone-exposed groups. Adult DEX3 offspring also showed increased corticotrophin-releasing hormone mRNA with unaltered glucocorticoid receptor mRNA in the hypothalamic paraventricular nucleus and reduced hippocampal glucocorticoid- and mineralocorticoid receptor mRNA expression, suggesting reduced hippocampal sensitivity to glucocorticoid suppression of the stress axis. In contrast, DEX1-3 rats had no changes in hippocampal corticosteroid receptors, but showed increased mRNA levels for both receptors in the basolateral nucleus of the amygdala. From this data we suggest that prenatal glucocorticoid exposure programs behavioural inhibition perhaps via increased amygdalar corticotrophin-releasing hormone levels, while DEX3 also impairs coping and learning in aversive situations, possibly via altered hippocampal corticosteroid receptor levels. Overexposure to glucocorticoids, especially late in gestation, may explain the link between reduced early growth and adult affective dysfunction.

Adaptation, Psychological↗